Rifled gun barrel with tapered chromium bore wall



Aug. 3 1954 v. A. LAMB ETAL RIFLED GUN BARREL WITH TAPERED CHROMIUM BORE WALL v gvwcm fo'vs, Vernal-L A- Lamb Elhurt F. ElsburrL Filed Oct. 31, 1949 @ZR RQU to 02% Patented Aug. 31, 1954 RIFLED GUN BARREL WITH TAPERED CHROMIUM BORE WALL Vernon A. Lamb, Garrett Park, Md., and Elburt F. Osborn, State College, Pa., assignors to the United States of America as represented by the Secretary of the Army Application October 31, 1949, Serial No. 124,588

3 Claims.

, l The present invention relates to guns and more particularly to gun barrels having increased accuracy-life as compared to that of the usual standard barrel.

Gun barrels, particularly 0 caliber aircraft barrels and other barrels for rapid fire made in accordance with our invention display improved accuracy during repeated long bursts and extraordinarily long accuracy-life as compared with corresponding standard barrels. Our invention resides in providing adjacent to the muzzle of the barrel a metallic bore surface sufficiently hard to withstand plastic deformation at rapid firing temperatures and which defines a bore sufficiently constricted as to ensure projectile engagement with the rifiing of the barrel adjacent the muzzle even though this portion of the barrel be operating in thermally expanded condition.

Hardening of a steel barrel, at least along the points of constriction, such as nitriding or induction hardening to obtain a hardness in excess of about 30 Rockwell C or the deposition of a hard chromium plate prevents deformation at the points of constriction. For superior results an adherent plate of hard chromium is provided over a nitrided or otherwise hardened steel bore surface by electrodeposition. The plate may extend from the breech or from points intermediate the muzzle and breech, as for example the forcing cone to give a substantially cylindrical constricted bore or a bore having a forwardly converging constricting taper, or for example, only over a relative short length of barrel adjacent the muzzle to constrict the muzzle sufliciently and provide compensation for circumferential expansion due to the excessive heat created during rapid fire. The chromium in addition to being resistant to plastic deformation is more resistant to erosion than is hardened or soft gun steel.

It has been found best for practical purposes to employ a plate in such a manner to produce a forwardly converging constricting taper. This usually ensures a lower starting pressure in firing than does a cylindrical constricted bore and serves to alleviate the blowing of primers. On the other hand, the cylindrical constricted bore is satisfactory when deep rifiing grooves as compared with grooves in a standard barrel are employed particularly toward the breech. A short length of constricting plate at the muzzle is not preferred because the plate usually is removed progressively forward by engraving.

Gun barrels provided with muzzle chokes of the character of our invention have amazing long accuracy-life. The barrels were fired until they were red hot on the outside and until the bore from the origin to a foot or so from the muzzle were severely eroded and still the barrels fired accuratelyoften firing more accurately toward the end of a long firing program than at the beginning.

An important object of the present invention is to provide standard gun barrels with means to greatly increase accuracy-life.

Another object of the invention is a gun barrel having a hardened bore with a surface electrodeposited to form a cylindrical constricted bore providing projectile engagement with the rifiing when operating in thermally expanded condition.

Another object of the invention is a gun barrel having a forwardly converging taper of hard metal adjacent to the muzzle to compensate for circumferential expansion of the muzzle.

In the accompanying drawings, which form a part of this specification and wherein like characters of reference denote like parts throughout,

Figure 1 is a longitudinal section of a gun barrel showing an embodiment of the invention illustrating the cylindrical constricted bore.

Figure 2 is an enlarged longitudinal sectional view adjacent the muzzle illustrating the forwardly converging taper adjacent the muzzle.

Figure 3 is a sectional View taken along line 33 of Figure 2.

In Figure l of the drawings, wherein for the purpose of illustration is shown one embodiment of the invention, the numeral i designates a gun barrel having a bore 2 which is normally rifled. The entire surface of the bore between the muzzle and forcing cone 2a or a portion of the length thereof is hardened as indicated at 3, and a relatively thin metallic plating 4, of a suitable erosion resistant material such as chromium is applied to the hardened surface 3. The bore of the gun may be hardened by means such as high frequency induction heating or by nitriding. The chromium may be deposited on the hardened surface electrolytically. In the exercise of our invention a muzzle choke is produced by carefully thickening the plating 4, resulting in a forwardly converging constriction toward the muzzle greatly increasing the accuracy-life as compared to that of the standard barrel. When the entire length of the bore between forcing cone 2a and the muzzle is provided with a tapered plating it becomes necessary to deepen the grooves to lessen the chance of high pressure due to the constriction at the breech.

Figure 2 of the drawings illustrates another embodiment of our invention wherein the plate 4 begins at a point intermediate the muzzle and breech, as shown by reference numeral 5. The bore of the gun is hardened as indicated by reference numeral 6. The plate 4 is gradually thickened toward the muzzle so as to provide a constricted section adjacent the muzzle sufficiently hard to withstand plastic deformation and to ensure projectile engagement with the rifling '1, when the section is operating in thermally expanded condition resulting in a great increase in accuracy-life.

We claim:

1. A rifled gun barrel having a hardened cylindrical bore surface and including means forming a forcing cone adjacent the breech end, a tapered chromium bore wall deposited on said hardened surface and extending from said forcing cone to said muzzle end, said wall increasing in thickness progressively toward said muzzle end to define a bore slightly constricted to compensate for thermal expansion under peak operating temperatures and to insure intimate engagement with the sur face of a fired projectile.

2. A rifled gun barrel having a hardened cylincal bore surface and including means forming a forcing cone adjacent the breech end thereof, a tapered chromium bore wall deposited on said hardened surface intermediate said forcing cone and said muzzle end and extending to said muzzle end, said wall increasing in thickness progressively toward said muzzle end to define a bore slightly constricted to compensate for thermal expansion 4 under peak operating temperatures and to insure intimate engagement with the surface of a fired projectile.

3. A rifled gun barrel having a hardened cylindrical bore surface, a tapered chromium bore wall deposited on said hardened surface for a predetermined short distance rearwardly of the muzzle end thereof, said wall increasing progressively in thickness toward said muzzle end and defining a bore slightly constricted to compensate for thermal expansion under peak operating temperatures and to insure intimate engagement with the surface of a fired projectile.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 660,496 Evans Oct. 23, 19 0 1,127,268 Malster Feb. 2, 1915 1,546,895 Hedin July 21, 1925 1,886,218 Olin Nov. 1, 1932 1,944,333 Gerlich Jan, 30, 1934 1,997,004 Morris Apr. 9, 1935 2,345,089 Born Mar. 28, 1944 2,395,044 Gorton Feb. 16, 1946 FOREIGN PATENTS Number Country Date 238,379 Great Britain Aug. 20, 1925 Great Britain Dec. 18, 1945 

